Obsessive-Compulsive Disorder (OCD) is a prevalent problem with important public health implications. OCD affects 2 to 3% of Americans, and is associated with substantial impairment, and direct and indirect economic costs. Nearly 75% of individuals with OCD fail to access treatment and individuals that do access treatment are often left with substantial residual symptoms even after successful treatment. Therefore, empirically-based programs to prevent the development of full-blown OCD would hold great promise in mitigating the negative impact of this disorder. However, a better understanding of the etiology of OCD is needed to inform the development of these prevention programs. SPECIFIC AIMS: Cognitive theories are among the most influential models of OCD. These models propose that negative interpretations of intrusions and stress confer vulnerability to OCD. However, etiological predictions from these models remain untested. The proposed study is innovative in prospectively testing predictors of OC symptom changes hypothesized by cognitive models. DESIGN AND HYPOTHESES: This new investigator initiated R03 will use a sample of 500 young adults during a period of increased stress to test the hypotheses that maladaptive OC-related beliefs, stress (negative life events), and their interaction, will prospectively predict changes in OC symptoms over six months. Further, it is hypothesized that initial OC-related beliefs will significantly more strongly predict changes in OC symptoms than changes in depressive symptoms. A supplementary aim will test the hypothesis that the core study measures will perform similarly when administered via a computer compared to traditional paper and pencil administration, facilitating future longitudinal studies of OCD. SIGNIFICANCE: The proposed study represents an initial step along a line of research clarifying the role of psychosocial factors in the etiology of OCD. If OC-related beliefs and stress prospectively predict increases in OCD symptoms, these variables could be targeted in preventative interventions. Empirically based prevention programs hold great promise for stopping the development of full-blown OCD and eliminating years of needless suffering. Documentation of the feasibility of computer-based administration of study questionnaires would greatly facilitate future longitudinal research on OCD.